1. Field of the Invention
The invention relates to a thin film semiconductor device and a method of manufacturing the same and to a display of an active matrix type configured of a thin film semiconductor device. In more detail, the invention relates to a crystallization technology of a semiconductor thin film for forming a device region of a thin film semiconductor device. In further detail, the invention relates to a lateral crystal growth technology for applying a temperature difference to different regions of a semiconductor thin film by laser annealing and inducing crystal growth in a planar direction (lateral direction) of the film by utilizing it.
2. Description of the Related Art
A thin film semiconductor device employs a thin film transistor as a major configuration device. The thin film transistor uses a semiconductor thin film as an active layer. As the semiconductor thin film, for example, a silicon film is generally used. In recent years, a technology for forming a polycrystalline silicon film on a cheap glass substrate to form an active layer of a thin film transistor is being developed.
As the technology for forming a polycrystalline silicon film on a glass substrate at a low temperature, a crystallization technology by irradiation with laser light is developed. The crystallization by irradiation with laser light (hereinafter sometimes referred to as “laser annealing”) is a technology for absorbing energy of laser light onto an amorphous silicon film to instantaneously melt only the film and recrystallizing it in a cooling process.
Recently, a technology for obtaining a polycrystalline silicon film with high crystallinity by using continuous oscillation laser light is reported. This technology is a technology for scanning continuous oscillation laser light on an amorphous silicon film, moving a solid-liquid interface of a semiconductor thin film in a lateral direction to make a temperature difference in the film and causing lateral crystal growth in the silicon film by utilizing this temperature difference. However, in view of the point that if a scanning speed is low, the film itself causes bumping and disappears, whereas if the scanning speed is high, it exceeds the movement speed of the solid-liquid interface so that the lateral crystal growth becomes insufficient, this technology is narrow with respect to a process margin.
A lateral crystal growth technology utilizing pulse oscillation laser light instead the continuous oscillation laser light is developed and described in, for example, JP-A-2003-318108 (Patent Document 1). In this Patent Document 1, an amorphous silicon film is formed on a substrate, and a metal film is further formed on a part of the amorphous silicon film. By using this metal film as a mask, first irradiation with laser light is performed from an upper part of the amorphous silicon film, thereby crystallizing a portion other than the part of the amorphous silicon film masked by the metal film. Thereafter, the metal film is removed, and second irradiation with laser light is performed from an upper part of the amorphous silicon film, thereby crystallizing the part of the amorphous silicon film by means of lateral growth. A polycrystalline silicon film having been crystallized by the second irradiation with laser light is used in a channel region of a thin film transistor. Besides, a technology which is not a lateral crystal growth technology but a technology for crystallizing a silicon thin film by double irradiation with excimer laser light to convert it into a polycrystalline silicon film is described in JP-A-2001-102589 (Patent Document 2).